Preparation and evaluation of some nanocarbon (NC) based composites for optoelectronic applications

Polyaniline/nanocarbon (PANI/NC) nanocomposites have been prepared by in situ polymerization of aniline monomer in the presence of a stable colloidal solution of nanocarbon NC using ammonium persulfate as an initiator and silver ions (Ag+) as oxidizing agents to produce PANI/NC and PANI/NC/Ag2O nanocomposites, respectively. The morphological studies of the formed nanocomposites have been elucidated via transmission and scanning electron microscopes (TEM and SEM). Further characterization of the prepared nanocomposites has been done via infrared spectroscopy (IR), X-ray diffractometer (XRD), X-ray photoelectron spectroscopy (XPS), particle size distribution analysis (PSD), fluorescence microscope (FM), UV–VIS spectroscopy, and finally surface analysis. XRD results confirmed the presence of silver oxide Ag2O nanoparticles, and the obtained data is well matched with the JCPDS card number 76–1393 of silver oxide. XPS analyses have shown two prevailing characteristic peaks for Ag 3d5/2 and Ag 3d3/2 at 367.1 and 373 eV, respectively, representing Ag2O nanoparticles, which are matchable with the XRD analysis. The PSD analysis revealed that the sizes of the prepared nanocomposites are in the size range from 60 to 140 nm. The FM measurements showed luminescence from the prepared nanocomposites upon irradiation with different lights. This recommends that the fluorophores present in the prepared nanocomposites have the potential to both absorb and emit light. The AC conductivity and the dielectric permittivity of the obtained nanocomposites at room temperature and at different frequency ranges have been investigated. At higher frequency ranges, the maximum ac conductivity obtained was 1.06 × 10–2 and 2.5 × 10–2 S.Cm-1 for the PANI/NC and PANI/NC/Ag2O, respectively. As far as we know, these new nanocomposites with superior optical and electrical characteristics have not been described yet in the literature.

The compounds known as polymeric nanocomposites contain nanoparticles like nanofillers. The nanofillers may be of many types and forms, but at least one of their sizes must fall below 100 nm. Soot, graphene, carbon nanotubes, and graphene may all be examples of nanofillers [1][2][3] .
The tight requirements of managing the filler's dispersion into the matrix and further stabilizing the resulting compound guide technologies for nanocomposite creation. Recently, research has been focused on carbonaceous nanofiller materials, like grapheme nanoplatelets (GNPs) and carbon nanotubes (CNTs) [4][5][6] . CNTs are a class of nanomaterials that provide a variety of uses because of their high aspect ratio, large surface area, and unique electrical, thermal, and optical properties 1,7 . CNTs are strong like a diamond while being light, thermally and electrically conductive, and formable like graphite.
One category of hybrid materials is called conducting polymer nanocomposites, which comprise of an inorganic element with at least one dimension in the nanoscale range and a polymer matrix (conductive polymer). Conducting polymer nanocomposites are a group of materials with significant applications in an assortment of electronic devices, such as light-emitting diodes, batteries, photovoltaics, and sensors [8][9][10][11] .
For the formation of the nanocomposites, a variety of preparation methods have been used, including the microemulsion, sol gel method, and chemical oxidative process 12 .
Conducting polymer nanocomposites have attracted the attention of numerous researchers due to their well-known unique optical and electrocatalytic properties. Molecules like dyes, carbazole compounds, and www.nature.com/scientificreports/ done using (TGA; PerkinElmer (Germany) at a temperature range of 0-500 °C with a heating rate of 10 °C min −1 in a nitrogen atmosphere.
Surface analysis. The specific surface area, and pore size distribution of the prepared samples have been determined from nitrogen adsorption-desorption isotherms by a high-speed gas sorption analyzer (NOVA 2000 series, chromatic, UK) at 77 K. Before measurements, the samples were out-gassed at 150 °C in vacuum for 6 h. The pore size distributions were derived from the NLDFT method. The total pore volume was estimated from the amount of gas adsorbed at the maximum relative pressure.
Cyclic voltammetry measurements. According to Elhalawany et al. 37 , the electrochemical behaviour of the produced nanocomposites was accomplished utilising an Autolab Potentiostat/Galvanostat 302N. Software has been used to monitor the I-V curves. The redox potentials Eox and Ered are calculated using ferrocence material as a reference.
Electrical measurements. Agilent E4991 B 1 M-1G impedance material analyzer, USA, was used to test the produced nanocomposites' ac conductivity in the frequency range of 0.1 Hz to 10 MHz at room temperature.

Results and discussion
For a variety of applications, PANI/NC and PANI/NC/ Ag 2 O nanocomposites with improved electrical and optical properties have been well prepared in this study effort. There has been put forth a viable mechanism for PANI polymerization in the presence of NC colloidal solution. Here is the proposed mechanism: First, the CB aggregates were dissociated with the help of a powerful high-shearing effect homogenizer at 10,000 rpm to create a stable colloidal solution of nanocarbon NC 36 that serves as a template for the polymerization of aniline monomer using APS initiator, as shown in Fig. 1    www.nature.com/scientificreports/ they are slightly shifted owing to composite formation. The main PANI-related absorption peaks can be plainly observed in Fig. 2 at 1503 and 1633 cm -1 , although they are slightly displaced as a result of composite formation. These are thought to relate to phenazine-like units and o-coupled aniline units 39 . The peak at 1305 cm -1 , which is a defining feature of the typical PANI base, is attributed to C-N stretching close to a quinonoid ring 24 .
A new peak at 1490 cm -1 is also visible in Fig. 2 as a result of the presence of Ag 2 O nanoparticles 24,40 .
UV-VIS spectra. Figure 3 presents the UV-VIS spectra of the synthesised nanocomposites. The distinctive bands at 430 and 825 nm correspond to transitions that take place in the bezenoid and quinonoid structures of PANI, respectively 41 . A prolonged conjugation, a mixed valence system, or both may be responsible for the appearance of a new peak in the near infrared at 960 nm 42 . The presence of Ag 2 O nanoparticles causes the PANI/ NC/ Ag 2 O nanocomposites to exhibit the same peaks with a minor shift. A crucial indicator of the produced nanocomposites' electrical conductivity is their optical band gap (OBG). According to Tauc's law, the optical band gap OBG may be elucidated from the UV-VIS curve according to the following equation 43,44 : where α is the absorption coefficient, hυ is the energy of photons, Eg is the optical energy gap OBG and n is the exponent based on the type of electronic transitions.
The Eg values can be obtained from the graph of (αhυ) 2 versus hυ as shown in Fig. 4. The OBG has been deduced by continuing the straight line to (ahυ) 2 = 0. The deduced OBG values are 2.1 and 1.5 eV for PANI/NC and PANI/NC/Ag 2 O respectively. The optical band gap OBG has a direct relationship with the conductivity. As shown from the results, the PANI/NC/Ag 2 O nanocomposite has the most extreme results, which indicates improved optical as well as electrical characteristics.
(1) αhυ = (hυ − E g ) n  www.nature.com/scientificreports/ Particle size distribution analysis PSD. The percentage of particles of a particular size relative to all particles is known as the particle size distribution. The quantity, volume, etc., of the particle size distribution can be measured. The distribution of particle sizes Fig. 5 illustrates the PSD analysis of the prepared composites. The produced nanocomposites' particle sizes may be shown in the figure to be in the nanoscale range. One broad band in the size range of 80-140 nm is seen in the PSD curve for PANI/NC, whereas two broad bands in the size ranges of 60-100 and 100-140 nm are visible in the PSD curve for PANI/NC/ Ag 2 O.
Scanning electron microscope SEM. Figure 6a-c demonstrate the SEM analysis and energy dispersive x-ray EDX spectra of the prepared nanocomposites. The PANI/NC nanocomposite has adapted the flower-like structures, as seen in Fig. 6a. The deformed structures in Fig. 6b have bright patches that stand in for Ag 2 O nanoparticles. The elemental analysis of PANI/NC/ Ag 2 O using (EDX) is shown in Fig. 6c. Analytical identification of the elements (elemental composition) contained in any given substance is accomplished via energy dispersive X-ray spectroscopy (EDX) 1 . EDX is a measure to determine the elemental composition of the material. The beam that hits the sample will stimulate an electron in an inner energy level, causing its ejection and hence generating an electron hole. The electron from an outer energy level will be able to jump into this hole accompanied by X-ray emission. The energy of the emitted X-rays will be monitored by the aid of an energy dispersive for elemental composition elucidation. Figure 6c shows the EDX analysis for PANI/NC/Ag 2 O that give rise to a characteristic peak at 2.9 eV, which confirms the presence of silver.  www.nature.com/scientificreports/ Transmission electron microscope TEM. The produced composites' TEM graphs are displayed in Figs. 7a,b. As can be seen from Fig. 7a, the NC are randomly distributed across the PANI matrix in the form of black blotches. According to Fig. 7b, the inclusion of Ag 2 O nanoparticles caused the structure to assume the shape of spheres.
Fluorescence microscope. Fluorescence is the process through which a substance emits light after absorbing it. The wavelength of the emitted light is often longer than the wavelength of the absorbed light. The current fluorophores, which are in charge of light absorption, absorb light of a specific wavelength and emit light of longer wavelengths when a substance is irradiated by light (i.e., of a dissimilar color from the absorbed one). The optical response of the produced composites to light radiation was examined by the use of a fluorescence microscope examination. The prepared composites are exposed to incident light of different wavelengths from a fluorescence microscope in order to determine the associated changes in their electronic/optical states resulting from charge   www.nature.com/scientificreports/ separation and transport as a result of the incident light on them. Figures 8, 9 show the examination and illustration of the fluorescence characteristics of the created nanocomposites using a fluorescence microscope and three different wave lengths (blue, green, and red). Figures 8, 9 show that the nanocomposites emit nothing when exposed to blue light, yellowish brown when exposed to green light, and orange red when exposed to red light. This suggests that the produced nanocomposites contain fluorophores that are both light-absorbing and capable of longer-wavelength light reemission. These characteristics support their application in LEDs, solar cells, and electronic devices.
X-ray diffraction analysis (XRD). Figure 10a,b, represents the XRD analysis of PANI/NC and PANI/NC/Ag 2 O. Figure 10a shows broad peak at 2θ = 21 to 25 0 which attributed to the absorption peak for PANI/NC 45 . Figure 10a shows also a small intense peak at 2θ = 6.483 which is due to long PANI chains and more ordered structure 46 . Figure Fig. 11 showed two characteristic peaks at 284.2 eV and at 286 eV corresponding to the carbon atoms bonded to imine nitrogen (= N-) and amine nitrogen (-NH-), respectively 50 . In addition to these peaks the spectrum of the PANI/NC has an intense peak of N at 400.1 eV. NEXAFS investigation of reference compounds has revealed the intense sharp p-resonance between 397.4 and 397.7 eV in the N K-edge spectrum of emeraldine base and two peaks in the ranges 398.8399.1 eV and 402.1402.7 eV in the spectrum of emeraldine salts 51 . Thus, the peak at 400.1 eV in our spectrum are attributed to imine nitrogen (the splitting of p-resonance arises from conjugation effects 51 , the peak at 399.7 eV can be attributed to the protonated amine groups (-NH + -), while the peak around 402 eV is due to transitions within amine nitrogen in -NH-and/or -NH 2 -groups.
According to the literature survey, the location of the XPS peaks of silver depends on the chemical states of silver element and the size of the nanoparticles 52,53 . The binding energy of the. Ag(0) is higher than that of Ag(I), and the binding energy of Ag(0) in smaller clusters is higher than that in bigger nanoparticles. It was reported that small Ag nanoparticles readily react with oxygen, forming Ag 2 O and AgO upon exposure to air 54 .The binding energies of 368.0-368.3, 367.6-367.8, and 367.3-367.4 eV were reported for pure Ag, Ag 2 O, and AgO, respectively 55,56 . Figure 12 shows the narrow-range XPS spectra of PANI/NC/Ag 2 O composite. Two peaks for Ag 3d5/2 were observed at 368.2 and 367.1 eV, representing Ag0 and Ag 2 O particles, respectively, whereas the Ag 3d3/2 peaks were observed at 374.5 and 373 eV, representing Ag0 and Ag 2 O particles, respectively 57,58 . It is clearly seen from www.nature.com/scientificreports/ Thermo-gravimetric analysis (TGA). The thermogravimetric analysis (TGA) of pure PANI/NC and PANI/ NC/Ag 2 O nanocomposite is shown in Fig. 13 Surface analysis. The superiority of the materials is often specified by their surface area (SA), pore volume, mean pore diameter, and pore size distribution. The nitrogen isotherm data of the tested samples are displayed in Fig. 14. The samples are shown to be mesoporous in structure, and the adsorption curve seems to be an IUPAC type II curve. The pore size distributions (PSDs) of the samples under study are displayed in Fig. 15. According to IUPAC, pores with an internal width of less than 2 nm, in the range of 2-50 nm, and greater than 50 nm are considered micropores, mesopores, and macropores, respectively 36 . From the PSDs data displayed in Fig. 15, one can conclude that the tested samples are mesoporous. Table 1 outlines the estimated porous parameters of the samples. It can be seeing that NC sample has the highest surface area SA and the lowest pore size PS. However, the SA and the PS of the PANI/NC and PANI/NC/ Ag 2 O samples are decreased slightly. This finding indicated that the presence of PANI or PANI/Ag 2 O doesn't affect the mesoporous structure of NC.

Cyclic Voltammetric measurements. By measuring the oxidation and reduction potentials (E ox & E red )
of the chemical material, cyclic voltammetry (Cv) plays a significant role in monitoring the oxidation and reduction reactions. Thus, using the recorded data, the energy band gap E g can be determined (E ox & E red ). The result of subtracting the energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) yields the energy band gap E g . www.nature.com/scientificreports/ The HOMO is regarded in solid state physics as the energy needed to eliminate an electron by oxidation. The LUMO is the opposite, since it provides the energy required for the reduction process, which inserts an electron. Cyclic voltammetric measurements can be used to analyze these oxidation-reduction processes.
The prepared nanocomposites' cyclic voltammogram CV of the current-voltage I-V curve is displayed in Fig. 16. Due to the electrochemical oxidation and reduction events that took place, Fig. 16 depicts typical peaks in the anodic and cathodic branches of the CV curve for PANI/NC and PANI/NC/Ag 2 O, respectively.  .72 eV respectively. The energy band gap E g can be assumed to be 1.21 and 0.98 eV for PANI/NC and PANI/NC/ Ag 2 O, respectively, because it is equal to the difference between the HOMO and LUMO energies. These prominent electrical and optical characteristics are indicated by the low E g values.
All polymers' electrochemical energy band gaps E g are invariably less than those estimated from UV-VIS spectra 59 . Although it has been studied in the literature, the discrepancy between the energy gab E g and the optical energy gap E opt still requires a full study.     www.nature.com/scientificreports/ Electrical conductivity measurements. Conjugated polymers' conductivity is one of their most important features for a variety of applications. Such polymers' conductivity is attributed to the generation of polarons and bipolarons, the dominant charge carriers. The radical cation with the accompanying lattice distortion that creates a positively charged hole site is known as a polaron. This hole site is conductive due to its mobility within the polymer conjugation system. These polymers often use charge carrier hopping as their conduction mechanism 24,32 .
Conducting polymers typically have an energy gap Eg separating their occupied valence band from their vacant conduction band. These polymers can be doped to improve the oxidation-reduction processes, which leads to the formation of new energy levels in the energy gap and hence enhancement in conductivity 60 .
Carbon black's filled polymers are considered conductors; at room temperature, their conductivity ranges from 0.1 to 102 S/cm 1 . Above a certain concentration, carbon black-filled polymers become conductors. As a result, carbon blacks are frequently utilised as fillers in polymers for uses including conductive packaging for electronic components and conductor shield composites for cables 2 .
The ac conductivity of synthesized pure PANI/NC and PANI/NC/Ag 2 O at room temperature has been examined at frequency ranges from 0.1 Hz to 10 MHz. Capacitance Cp and conductance G values have been noted using the LCR Bridge.
At room temperature, Fig. 17 depicts the relationship between ac conductivity fluctuation and angular frequency variation for the synthesized nanocomposites. Figure 17 showed that the ac conductivity rose with frequency and was significantly higher in the silver-doped nanocomposite (PANI/NC/Ag 2 O) than in PANI/NC. Ag 2 O nanoparticles are thought to be responsible for this increase in ac conductivity since they make charge transfer much easier.
And as predicted by XRD analysis, Ag 2 O nanoparticles have increased the crystallinity of the resulting composite, and as a result, their chemical structure has become more ordered and their electrical conductivity has increased 61 .
According to Fig. 17, the maximum ac conductivities for the PANI/NC and PANI/NC/ Ag 2 O nanocomposites are 1.06 × 10 -2 and 2.5 × 10 -2 S.cm -1 respectively.  www.nature.com/scientificreports/ The development of new energy levels in the band gap area, which makes it easier to transmit charges, is the likely cause of this increase in conductivity 62 .
In general, the following equation describes how the ac conductivity of polymers evolves with frequency: where A is a constant that is typically temperature-dependent, ω is the angular frequency (ω = 2*π*f) and S is the frequency exponent, which typically falls between 0 and 1. The hopping mechanism and the observed behaviour of (S) are compatible. According to the hopping model, electrical conduction happens through a process called bipolaron hopping, in which two polarons instantly hop or jump over a potential barrier between two charged states. The height of the barrier is related to the separation of the formed polarons via a columbic interaction. This is consistent with our findings, which show that the inclusion of NC and Ag 2 O nanoparticles improves the transitions of the polarons that are generated and, as a result, increases conductivity. Dielectric properties. The measured capacitance value has been used to compute the dielectric constant at room temperature. The following equation was used to get the dielectric constant (ε′): where A is the cross sectional area, (ε ο ) is the free space permittivity, and Cp is the capacitance. Figure 18 depicts the relationship between the dielectric constant (ε′) and angular frequency Ln(ω). Figure 18 demonstrates that (ε′) drops as frequency increases. This may be attributed to the inability of the formed dipoles to adapt themselves to be in the same direction of the applied electric field 32 . As a result, it is anticipated that the tendency for polarization to decrease with increasing frequency will also occur.
The results revealed that the dielectric constant (ε′) of the silver dopped nanocomposite is much higher than that of PANI/NC at all frequencies. This increase is attributed to molecules' polarizations when exposed to an applied electric field, where the dielectric permittivity of the material depends on the extent of polarization of the molecules 63 .
It can be concluded that the existence of NC and Ag 2 O nanoparticles in the formed composites enhances the dielectric permittivity due to enhanced polarization.
The findings demonstrated that at all frequencies, the dielectric constant (ε′) of the silver-doped nanocomposite is much higher than that of PANI/NC. This rise is attributable to the polarisation of the molecules in an electric field, where the degree of polarisation of the molecules determines the material's dielectric permittivity, i.e., the greater the degree of polarisation, the higher the permittivity 63 .
One can conclude that the interfacial polarisation that results in an increase in dielectric permittivity is due to the inclusion of NC and Ag 2 O nanoparticles in the produced composites to enhance the dielectric permittivity.

Conclusion
The successful preparation of PANI/NC and PANI/NC/ Ag 2 O nanocomposites has been accomplished employing a high shearing effect homogenizer and a chemical oxidative approach. According to the PSD and TEM analysis the sizes of the prepared nanocomposites are in the range of 60-140 nm. The EDX analysis revealed a typical silver nanoparticle peak, confirming the doping procedure. XPS and XRD analysis confirmed the presence of Ag 2 O nanoparticles. According to the observations made using a fluorescence microscope, the produced nanocomposites displayed luminescence when exposed to various wavelengths of light. This suggests that the prepared nanocomposites contain fluorophores with the ability to both absorb and emit light. The maximum www.nature.com/scientificreports/ ac conductivities for the PANI/NC and PANI/NC/ Ag 2 O nanocomposites, respectively, were 1.06 × 10 -2 and 2.5 × 10 -2 S.cm -1 . A concept for their future usage in optoelectric devices like solar cells is generated by their improved optical and electrical capabilities. Finally, it can be said that the created nanocomposites are characterized by easy processing and low cost, and this will open up new possibilities for the technology of nanocomposites and their many applications, particularly in optoelectric devices like solar cells.

Data availability
The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.